There are many techniques and products for browsing and representing photo collections. The majority
uses a 2 dimensional representation of the collection on screen but a few make some use of the third
dimension.

\cite{bppl} introduced a user-centric system for visualization and layout for content-based image 
retrieval. This system assists the user in organizing photo sets by adaptively learning the preferences
of the user.

\cite{quilt} proposed a novel layout called time quilt. The time quilt layout let zoomable photo 
browsers support time-based visual search tasks more effectively and over large collections.

Both of these systems only use a 2D representation of images. They both address to some extent the
problem of intuitively laying out photos but their emphasis is on a specific algorithm as opposed to
our focus of having a pluggable mechanism for rendering a multitude of layouts. The algorithms described 
in the above papers would without a doubt be a great addition to the pr3Da layout collection.

Cooliris (formerly PicLens) \cite{cooliris} is a browser plugin that transforms your browser into an 
interactive, full-screen "cinematic" experience for web media. A 3D wall is created and displays pictures 
that are loaded from various sources like Google Images, Flickr and Youtube. This system does use a three
dimensions to display photo collections and emphasis is on the visuals only. They do not attempt to use
the third dimension to convey any information about the pictures nor do they provide an API to use their
rendering engine for other applications as is the main purpose of pr3Da.

In \cite{ptourism} the authors describe a system for browsing photos in three dimensions. This system uses
content based algorithms to match images and arrange them in 3D space. It relies on overlapping of visual 
picture content and can only be used for location based browsing. They do implement some impressive
transition algorithms that might be of use in pr3Da.

Many more systems exist for this purpose and it would be too big of a task to mention them all here.
None of those we found addressed the needs that we are trying to fulfill with pr3Da, to have a visually
pleasing API capable of rendering collections of pictures in configurable ways in a virtual environment.
